Browsing by Author "Lin, Chun"

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Exploring nature-based solutions to control stormwater in an urban area
(2021-12-13) Lin, Chun
Insinööritieteiden korkeakoulu | Master's thesis
Under urban densification and climate change, cities are facing stormwater management challenges such as disruptive water balance and excessive surface runoff generation over impervious surfaces. Nature-based solutions provide alternative to supplement traditional stormwater system in order to mitigate negative impact from urban impermeable space. This study aims to model stormwater scenarios with nature-based solutions in Otaniemi campus, and to evaluate how nature-based solutions can mitigate negative impacts of urban densification. The first objective is to establish a hydrological model and assess the current surface runoff conditions. The second objective is to establish an alternative set of Low Impact Development (LID) controls for representing nature-based stormwater management solutions and evaluate whether they can compensate for negative impact of urbanization in long term water balance and under extreme storm events. Otaniemi campus in Espoo was chosen as the study site, divided into testing catchment (TS) and reference catchment (RE), with former having 23%-units more impervious surface. Established from available spatial data and rainfall data, rainfall-runoff simulations were produced in US EPA Storm Water Management Model (SWMM). LIDs were implemented both individually and in combined scenarios representing NBS in catchment TS. The model was run in 4 different rain intensity design storms of 10mins duration, and later in long term simulation in wet summer 2005 and dry summer 2006. Results show that individual LID controls were capable of reducing surface runoff and diminishing outfall peak flow rate. Yet it did not change peak flow rate pattern nor delay the peak. In long term simulations and design rainfall events, permeable pavement provided biggest runoff reduction, while bioretention and vegetated swale were the most effective per LID unit area. More significant impact was observed in the results of LID combinations, which impact amplified from low to high intensity of LID combination scenarios. In medium LID intensity, runoff volume was significantly reduced to similar level as in the less developed area RE. In high LID intensity, runoff volume was reduced to be lower than RE. Flooding was non-existent under 50 years return period of design rainfall. Therefore, permeable pavement is recommended if large amount of runoff reduction is to be achieved. Bioretention and vegetated swale are preferred when NBS size is limited. Combination of LID performs the best not only in runoff reduction but also in slowing outfall flow rate and delaying the peak time. As part of the stormwater management NBS brings multiple benefits more than improvement of stormwater, including microclimate, urban green space and biodiversity.
Water resilient urbanity - spatial study and design for urban flood
(2015) Lin, Chun
School of Arts, Design and Architecture | Master's thesis
Can water resilience in dense urban environment act as catalyst in urban regeneration? How does it play with spatial planning and urban synergy? Confronted by challenge of global climate change, urban cities that suffering from heavy downpour with high density built up space, are seeking strategy against flooding problem more than ever. Flooding issue often comes with distant city infrastructure network that it requires strategy being designed and implemented in a regional scale. As a result, cities dealing with urban flood, especially those not from sea-rising but from rain water overflow, their planning strategy relies on a larger level to take effects. It brings landscape-driven city making along with water infrastructures as important roles for spatial planning, while neighborhood scale of adaptive buildings enhance a city's ability for urban water resiliency. Guangzhou, the most prone city in China towards urban flooding problem, one of its oldest and most dense area En Ning is used as a testing ground. The urban design strategy is for the development of water resiliency in urbanity that is undergoing accelerating change and capacity demands. Design addresses in planning level driven by water landscape as urban framework, and envisions different urban growth for future layout. Integration of adaptive buildings and their structure strengthen the resilient ability with user engagement in spatial dimension.